Fish Managers Still Pushfor End to McNary 1 Percent Tests

by CBB Staff
Columbia Basin Bulletin - May 28, 2004

Research at McNary Dam was scaled back this week as biologists worried that a test which operates turbines above the 1 percent peak efficiency range required by the NOAA Fisheries 2000 Biological Opinion is causing excessive descaling and mortality among juvenile salmon migrating through the dam.

Last week salmon managers at the Technical Management Team meeting asked the U.S. Army Corps of Engineers to cease the Vertical Barrier Screen (VBS) tests, which require operation of turbine units at the dam outside the 1 percent range.

Although the Corps and salmon managers took another look at the test data at a meeting of the Walla Walla Fish Facility Design Review Workgroup (FFDRWG) May 19 and 20, and decided that an updated analysis showed smaller increases in mortality and descaling, salmon managers continued to push for an end to the studies. FFDRWG is made up of engineering and biological staff from the Corps and other state, tribal, and federal agencies.

The Corps agreed instead to scale back the tests, according to Mark Smith of the Corps.

"The Corps of Engineers led a discussion of these results and suggested that the levels of descaling are similar to past years and are not of great concern," Smith wrote in a memo to TMT this week. "However, the Corps did explain that due to initial testing, only 1-2 units were being considered for further testing, and based on the above analysis, risks to the run at large were low."

The Corps had determined that the differences in sampling methodology between the 3-hour sampling for the tests and the normal 24-hour sampling performed at the dam had been skewing the results and showing higher descaling and mortality when the turbines in the test were operating above the 1 percent efficiency limit.

"It was suggested that only the 24-hour sample be used for this analysis since the 3-hour sample might have some inherent bias in estimates due to sampling methodology," Smith wrote.

The 24-hour only sampling showed descaling of 4.6 percent and mortality of 0.3 percent when operating within the 1 percent efficiency limit. With one unit at the dam operating above the limit, descaling was 3.6 percent and mortality was 0.1 percent. That rose to 7.5 percent and 0.3 percent respectively with two units operating above the limits, and to 7.0 percent and 0.4 percent with four units running, according to Smith's information. The initial study proposal called for testing of four turbines above the 1 percent limit to evaluate three VBS units.

Descaling this year when the units have been running within the 1 percent efficiency limit ranged widely from 1.2 percent up to 9 percent, Smith said, adding that the Corps is proposing to use a 5 percent limit in descaling as it recommends further tests. If descaling is less than 5 percent, the Corps will continue limited studies this year.

"This information is critical in estimation of effects of turbine operation on fish guidance," Smith wrote. He said follow-up meetings at FFDRWG are expected this week.

The BiOp's reasonable and prudent alternative (RPA) number 58 calls for turbines to be operated within the 1 percent peak efficiency range during spring and summer while juvenile salmon migrants are in the river. The operating limits were set as a result of studies in the 1980s that determined turbine efficiency and fish survival are directly related.

After re-evaluating those studies, BPA concluded that operating outside the 1 percent efficiency limit at McNary may not result in survival different than operating within the 1 percent limit. If the dam can operate outside the 1 percent limit, it could spill less water and put more water through turbines to generate as much as $5 million more electricity each year in an average water year, BPA has said.